Conventionally, there has been known a Karman vortex flowmeter that measures a flow rate by generating Karman vortexes corresponding to a flow of a fluid, detecting them, and converting them into an electrical signal (for example, refer to Japanese Unexamined Patent Application, Publication No. Hei 9-196722).
The Karman vortex flowmeter disclosed in Japanese Unexamined Patent Application, Publication No. Hei 9-196722 forms a diaphragm around a thin plate-shaped pressure-receiving plate to fix it to a pipe included in a flow passage, and detects vibration of the pressure-receiving plate due to the Karman vortexes by a vibration pick-up element arranged in a hollow portion isolated from the flow passage by the diaphragm.